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David Traver e-mail: dtraver@ucsd.edu
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Utilizing zebrafish for new insights into the biology of hematopoietic stem cells
Hematopoietic stem cells (HSCs) exist as rare populations within blood-forming tissues that both self-renew and generate all blood cell lineages for life. HSCs have been isolated to relative purity in humans and mice, leading to a general understanding of their cellular and functional properties. Relatively little is known, however, of the genetic program underlying the embryonic development and subsequent maintenance of HSC fate. The development of zebrafish as a model system has introduced unbiased genetic approaches, such as forward genetic screens and high-throughput expression screens, to the study of vertebrate blood formation. Recent fluorescent transgenesis technology combined with the external fertilization and transparency of zebrafish embryos allows early events in HSC specification, maintenance, and differentiation to be easily observed. We are utilizing these advantages to fate map the earliest embryonic blood-forming cells. This will address many long-standing questions in the development of the immune system, including whether mesodermal derivatives give rise to blood precursors through hemangioblastic intermediates, cells believed to generate both blood and blood vessels, and whether embryonic and adult HSCs share common ancestry. In addition, we have developed a variety of cell sorting and transplantation methods to test HSC function.
Figure 1. Sorting and transplantation of LMO-2GFP cells from early zebrafish embryos. Approximately 8% of the cells in each embryo express GFP. After cell sorting, over 90% purity is attained and cells are tested for HSC function by transplantation into zebrafish blood mutants. HSC transplants can rescue the embryonic lethality in genetic mutants by rapidly generating erythrocytes.
Together, our work has established a cellular foundation upon which the genetic bases of stem cell function can be dissected. To this end, we are performing forward genetic and high-throughput expression screens to identify new gene functions in vertebrate stem cells. Novel genes that regulate HSC development, self-renewal, or lineage commitment will subsequently be examined for similar roles in mammalian systems. Furthermore, stem cell mutants may also show cancer predisposition since oncogenic transformation can be viewed as a reacquisition of stem cell characteristics, namely the abilities to self-renew and proliferate without apparent limit.
Akashi, K., D. Traver, T. Miyamoto, and I.L. Weissman. (2000). A clonogenic common myeloid progenitor that gives rise to all myeloid lineages. Nature 404:193-197.
Traver, D., K. Akashi, M. Manz, M. Merad, T. Miyamoto, E. G. Engleman, and I. L. Weissman. (2000). Development of CD8a-Positive dendritic cells from a common myeloid progenitor. Science 290:2152-2154.
Traver, D., and L. I. Zon. (2002). Walking the walk: migration and other common themes in blood and vascular development. Cell 108:731-734.
Langenau, D. M., D. Traver, A. A. Ferrando, J. Kutok, J. C. Aster, J. P. Kanki, S. Lin, E. Prochownik, N. Trede, L. I. Zon, and A. T. Look. (2003). Myc-induced T-cell leukemia in transgenic zebrafish. Science 299:887-890.
Traver, D., B. H. Paw, K. D. Poss, W. T. Penberthy, S. Lin, and L. I. Zon. (2003). Transplantation and in vivo imaging of multilineage engraftment in zebrafish bloodless mutants. Nature Immunology 4:1238-1246.
Traver, D., P. Herbomel, E. E. Patton, R. Murphy, J. A. Yoder, G. W. Litman, A. Catic, C. T. Amemiya, L. I. Zon, and N. S. Trede. (2003). The zebrafish as a model organism to study development of the immune system. Advances in Immunology 81:253-330.
Bertrand, J. Y., A. D. Kim, E. Violette, J. Cisson, and D. Traver. 2007. Definitive hematopoiesis initiates through a committed erythromyeloid progenitor in the zebrafish embryo. Development 134:4147-4156.
Bertrand, J. Y. , A. D. Kim, S. Teng, and D. Traver. 2008. CD41+ c-myb+ precursors colonize the zebrafish pronephros by a novel migration route to initiate adult hematopoiesis. Development 135:1853-1862.
David Traver received his Ph.D. in immunology from Stanford University where he received the McDevitt Prize for best thesis. He then completed postdoctoral studies at Harvard University as a fellow of the Irvington Institute. Since joining UCSD in 2004, he has received a Young Investigator Award from the Beckman Foundation, a Scholar Award from the American Society of Hematology and a New Faculty Award from the California Institute for Regenerative Medicine.
